The present invention relates to probes for application to selected areas of a subject's body for monitoring the physiological condition or changes thereof of a mammalian subject or detecting various medical conditions of the subject. The invention also relates to apparatus utilizing such probes, and also to methods utilizing such probes for detecting various medical conditions or physiological states.
The invention is particularly useful for the non-invasive detection of a medical condition or physiological state of a subject by monitoring changes in the peripheral arterial tone as described in U.S. Pat. Nos. 6,319,205, 6,322,515, 6,461,305 and 6,488,633, the contents of which are incorporated herein by reference, and in corresponding patents and applications filed in other countries, hereinafter referred to as the above-identified patents and applications. The invention is therefore described below with respect to the above-identified patents and applications, but it will be appreciated that various features of the invention could also be advantageously used in other probes and in the detection of other types of medical conditions or physiological conditions.
The above-identified patents and applications disclose various probe constructions, methods and apparatus for the non-invasive detection of a medical condition or physiological state of a subject, particularly by monitoring changes in the peripheral arterial tone as manifested by changes in the pulsatile arterial blood volume in a terminal extremity of a body part, e.g., a digit (finger or toe) of the subject. The various medical conditions detected by such probes, as described therein, include myocardial ischemia, sleep apnea and other sleep disordered breathing conditions, endothelial dysfunction (ED), and sleep disorders, as well as certain physiological states, such as mental stress, sympathetic nervous system reactivity, blood pressure, REM stage sleep, responses to physical, pharmacological or mental agents or stressors, etc.
In general, the probes described in the above-identified patents and applications include a housing defining at least one compartment for receiving the distal end of the subject's body part (e.g., a finger or toe), including its terminal-most extremity, such that the compartment is closed at one end and open at the opposite end, and a sensor for sensing a predetermined condition of the body part after received within the compartment. The preferred embodiments described therein are particularly useful for monitoring peripheral arterial tone in a subject's finger or toes, and for that purpose, they included pressurizing means for applying a static pressure field substantially uniformly around the distal end of the subject's finger, including its terminal-most extremity. The pressure field is of a predetermined magnitude sufficient to substantially prevent distention of the venous vasculature, to substantially prevent venous blood pooling within the applied pressure field, to substantially prevent uncontrolled venous backflow and retrogade shockwave propagation into the distal end of the finger, and to partially unload the wall tension of, but not to occlude, the arteries in the distal end of the finger when at heart level or below.
The prevention of venous pooling and venous distention is intended to prevent the occurrence of induced veno-arteriolar reflex vasoconstriction. The prevention of uncontrolled venous backflow and retrogade shockwave propagation into the distal end of the finger, and the partial unloading of arterial wall tension, contribute to the optimal measurement of arterial pulse signals divorced from venous volume changes and divorced from confounding induced reflex changes due to artifacts of the measurement method. The probe sensors described in the above-identified patents and applications were thus optimally configured to sense changes in the distal end of the subject's finger (or other body part) related to changes in volume therein due to pulsatile changes in instantaneous blood volume related to arterial tone.
It would be highly desirable to provide a probe allowing measurements to be made at a broader range of body sites. Such a probe could be used to facilitate the non-invasive determination of a wide range of physiological conditions, e.g., by comparing physiological changes at sites at which peripheral arterial tone are known to be governed by differing physiological control mechanisms. Such knowledge can, for example, allow for the discrimination between reflex mediated arterial tone changes and changes in arterial pulsatile amplitude due to mechanical hemodynamic consequences of reduced or otherwise changed cardiac stroke volume.
In addition to the advantages conferred by facilitating the measuring of peripheral arterial tone at a broader range of body sites, the ability to record a pulsatile arterial signal that is effectively divorced from venous blood changes, provides important advantages for the non-invasive measurement of blood oxygen saturation by the method of pulse oximetry. An important case in point is the application of such a probe to a measurement site overlying a superficial artery, wherein the level of blood oxygen may more accurately represent the actual systemic arterial oxygenation level than would measurements derived from sites overlying a vascular bed comprised largely of microvascular arterial and venous blood vessels. The combined, simultaneous, measurement of arterial blood saturation level and peripheral arterial pulsatile volume changes from the same probe would provide even greater diagnostic advantages.
Moreover, such a probe could be used at body locations better tolerated by the subject, or less likely to result in the subject removing the device, as is the case for a finger mounted probe, for example. Such a probe would also be useful for measurements on babies, young children, mentally compromised subjects, or subjects with structural or functional disorders of the fingers or toes.